This invention relates to intravascular catheters, and more particularly to endocardial ablation catheters and to their method of use in treating arrhythmia using radio frequency energy.
The heart is a muscular organ comprising four separate chambers which cooperate to pump blood throughout the body. The heart muscles must contract and relax in a coordinated sequence in order for blood to be passed through the circulatory system in an efficient manner. The heart includes a specialized system for generating impulses to cause rhythmical contraction of the heart muscle and for conducting these impulses rapidly through the heart. In the proper sequence the atria contract about one sixth of a second prior to ventricles. This enables extra filling of the ventricles before they contract to pump blood through the lungs and to other areas of the body.
The rhythmic impulse of the heart is generated in the sinoatrial node (SA node). The SA node has an inherent rhythm which can be modified by the sympathetic and parasympathetic nervous system. The impulse initiated by the SA node spreads through the atrium to the atrio-ventricular node (AV node), and then through the Purkinje fibers to the endocardial surfaces of the ventricles.
The rhythmical and conduction system of the heart is susceptible to disruption by disease. Such damage can result from the inability of the cardiac conduction pathways to properly transmit the electrical impulses generated in the SA node, leading to arrhythmias, or irregular heartbeats. Cardiac arrhythmias can often be detected through electrocardiograms.
Some forms of cardiac arrhythmia are able to be controlled through medication. However, other forms of arrhythmia do not respond to medication. Moreover, medication typically does not remedy the problem, and the dosage and the medication type must be changed periodically for continued control of the problem.
One alternative to medication is the surgical removal of a portion of the cardiac pathway which is responsible for the arrhythmia. The many dangers associated with open heart surgery render this a less preferred treatment option. Recently, however, it has become possible to intravascularly insert a specialized catheter within the heart, for positioning adjacent to the conduction tissue responsible for the arrhythmia. The catheter is adapted to deliver energy (e.g., radio frequency energy) to ablate or destroy the tissue from which the arrhythmia emanates. This has been found to be a relatively safe and effective technique for eliminating many forms of arrhythmia. Various ablation catheters and techniques for their use are described in U.S. Pat. Nos. 4,641,649; 4,785,815; 4,869,248; and 4,896,671.
Cardiac ablation catheters typically have at least one electrode at the distal end of the catheter which is adapted to deliver energy to the affected tissue. Other electrodes can be proximally positioned on the catheter and used for sensing endocardial signals. Ablation may be achieved by the application of electrical energy, such as radio frequency (RF) or direct current (DC) energy, from a generator source, through a conductor disposed within the catheter, and to the distal electrode.
During an ablation procedure it is essential to locate the distal, energy delivering electrode precisely at the site or sites of the arrhythmia. The proximal sensing electrodes aid in the proper positioning of the distal electrode. However, the sensing electrodes of the catheter often are in close proximity to the distal electrode, and to healthy cardiac tissue as well. The ablating energy usually travels through a conductor within the body of the catheter parallel and in close proximity to conductors attached to the sensing electrodes. Due to the need for minimal cross-sectional width and maximum flexibility of the catheter, the amount of insulating material which can encase each conduct is limited. Capacitive and/or inductive coupling can thus occur between these conductors when energy is supplied to the distal electrode. This capacitive effect can direct an unwanted amount of electrical current into the sensing electrodes. The delivery of this current, even in low levels, is potentially damaging to otherwise healthy tissue adjacent to the sensing electrodes. Moreover, the unwanted delivery of energy through the proximal electrodes reduces the amount of ablating energy which could otherwise be delivered through the distal electrode.
Accordingly, it is desirable to provide a catheter construction which minimizes the potential for delivery of energy through sensing electrodes used with an ablation catheter, and which maximizes the amount of energy delivered for an ablation procedure.
It is thus an object of the invention to provide an ablation catheter construction which minimizes the potential for inadvertently damaging healthy tissue during a cardiac ablation procedure. Another object is to Provide an ablation catheter which maximizes the amount of energy delivered through the distal electrode. Other objects will be apparent upon review of the disclosure which follows.